Simplify the following expression: $a = \dfrac{-r + 5}{3r} - \dfrac{-4r - 6}{3r}$
Since the expressions have the same denominator we simply subtract the numerators: $a = \dfrac{-r + 5 - (-4r - 6)}{3r}$ Distribute the negative sign: $a = \dfrac{-r + 5 + 4r + 6}{3r}$ Combine like terms: $a = \dfrac{3r + 11}{3r}$